# ------------------------------------------------------------------------------
# Copyright (c) Microsoft
# Licensed under the MIT License.
# Written by Bin Xiao (Bin.Xiao@microsoft.com)
# Modified by Ke Sun (sunk@mail.ustc.edu.cn)
# ------------------------------------------------------------------------------

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import os
import logging
import functools

import numpy as np

import torch
import torch.nn as nn
import torch._utils
import torch.nn.functional as F

BN_MOMENTUM = 0.1
logger = logging.getLogger(__name__)


def conv3x3(in_planes, out_planes, stride=1):
    """3x3 convolution with padding"""
    return nn.Conv2d(in_planes, out_planes, kernel_size=3, stride=stride,
                     padding=1, bias=False)


class BasicBlock(nn.Module):
    expansion = 1

    def __init__(self, inplanes, planes, stride=1, downsample=None):
        super(BasicBlock, self).__init__()
        self.conv1 = conv3x3(inplanes, planes, stride)
        self.bn1 = nn.BatchNorm2d(planes, momentum=BN_MOMENTUM)
        self.relu = nn.ReLU(inplace=True)
        self.conv2 = conv3x3(planes, planes)
        self.bn2 = nn.BatchNorm2d(planes, momentum=BN_MOMENTUM)
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        residual = x

        out = self.conv1(x)
        out = self.bn1(out)
        out = self.relu(out)

        out = self.conv2(out)
        out = self.bn2(out)

        if self.downsample is not None:
            residual = self.downsample(x)

        out += residual
        out = self.relu(out)

        return out


class Bottleneck(nn.Module):
    expansion = 4

    def __init__(self, inplanes, planes, stride=1, downsample=None):
        super(Bottleneck, self).__init__()
        self.conv1 = nn.Conv2d(inplanes, planes, kernel_size=1, bias=False)
        self.bn1 = nn.BatchNorm2d(planes, momentum=BN_MOMENTUM)
        self.conv2 = nn.Conv2d(planes, planes, kernel_size=3, stride=stride,
                               padding=1, bias=False)
        self.bn2 = nn.BatchNorm2d(planes, momentum=BN_MOMENTUM)
        self.conv3 = nn.Conv2d(planes, planes * self.expansion, kernel_size=1,
                               bias=False)
        self.bn3 = nn.BatchNorm2d(planes * self.expansion,
                                  momentum=BN_MOMENTUM)
        self.relu = nn.ReLU(inplace=True)
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        residual = x

        out = self.conv1(x)
        out = self.bn1(out)
        out = self.relu(out)

        out = self.conv2(out)
        out = self.bn2(out)
        out = self.relu(out)

        out = self.conv3(out)
        out = self.bn3(out)

        if self.downsample is not None:
            residual = self.downsample(x)

        out += residual
        out = self.relu(out)

        return out


class HighResolutionModule(nn.Module):
    def __init__(self, num_branches, blocks, num_blocks, num_inchannels,
                 num_channels, fuse_method, multi_scale_output=True):
        '''
        调用：
        # 调用高低分辨率交互模块， stage2 为例
        HighResolutionModule(num_branches, # 2
                             block, # 'BASIC'
                             num_blocks, # [4, 4]
                             num_inchannels, # 上个stage的out channel
                             num_channels, # [32, 64]
                             fuse_method, # SUM
                             reset_multi_scale_output)
        '''
        super(HighResolutionModule, self).__init__()
        self._check_branches(
            # 检查分支数目是否合理
            num_branches, blocks, num_blocks, num_inchannels, num_channels)

        self.num_inchannels = num_inchannels
        # 融合选用相加的方式
        self.fuse_method = fuse_method
        self.num_branches = num_branches

        self.multi_scale_output = multi_scale_output

        # 两个核心部分，一个是branches构建，一个是融合layers构建
        self.branches = self._make_branches(
            num_branches, blocks, num_blocks, num_channels)
        self.fuse_layers = self._make_fuse_layers()

        self.relu = nn.ReLU(False)

    def _check_branches(self, num_branches, blocks, num_blocks,
                        num_inchannels, num_channels):
        # 分别检查参数是否符合要求,看models.py中的参数，blocks参数冗余了
        if num_branches != len(num_blocks):
            error_msg = 'NUM_BRANCHES({}) <> NUM_BLOCKS({})'.format(
                num_branches, len(num_blocks))
            logger.error(error_msg)
            raise ValueError(error_msg)

        if num_branches != len(num_channels):
            error_msg = 'NUM_BRANCHES({}) <> NUM_CHANNELS({})'.format(
                num_branches, len(num_channels))
            logger.error(error_msg)
            raise ValueError(error_msg)

        if num_branches != len(num_inchannels):
            error_msg = 'NUM_BRANCHES({}) <> NUM_INCHANNELS({})'.format(
                num_branches, len(num_inchannels))
            logger.error(error_msg)
            raise ValueError(error_msg)

    def _make_one_branch(self, branch_index, block, num_blocks, num_channels,
                         stride=1):
        # 构建一个分支，一个分支重复num_blocks个block
        downsample = None

        # 这里判断，如果通道变大(分辨率变小)，则使用下采样
        if stride != 1 or \
           self.num_inchannels[branch_index] != num_channels[branch_index] * block.expansion:
            downsample = nn.Sequential(
                nn.Conv2d(self.num_inchannels[branch_index],
                          num_channels[branch_index] * block.expansion,
                          kernel_size=1, stride=stride, bias=False),
                nn.BatchNorm2d(num_channels[branch_index] * block.expansion,
                               momentum=BN_MOMENTUM),
            )

        layers = []
        layers.append(block(self.num_inchannels[branch_index],
                            num_channels[branch_index], stride, downsample))

        self.num_inchannels[branch_index] = \
            num_channels[branch_index] * block.expansion

        for i in range(1, num_blocks[branch_index]):
            layers.append(block(self.num_inchannels[branch_index],
                                num_channels[branch_index]))

        return nn.Sequential(*layers)

    def _make_branches(self, num_branches, block, num_blocks, num_channels):
        branches = []
        
        # 通过循环构建多分支，每个分支属于不同的分辨率
        for i in range(num_branches):
            branches.append(
                self._make_one_branch(i, block, num_blocks, num_channels))

        return nn.ModuleList(branches)

    def _make_fuse_layers(self):
        if self.num_branches == 1:
            return None

        num_branches = self.num_branches # 2
        num_inchannels = self.num_inchannels
        fuse_layers = []
        for i in range(num_branches if self.multi_scale_output else 1):
            # i代表枚举所有分支
            fuse_layer = []
            for j in range(num_branches):
                # j代表处理的当前分支
                if j > i: # 进行上采样，使用最近邻插值
                    fuse_layer.append(nn.Sequential(
                        nn.Conv2d(num_inchannels[j],
                                  num_inchannels[i],
                                  1,
                                  1,
                                  0,
                                  bias=False),
                        nn.BatchNorm2d(num_inchannels[i],
                                       momentum=BN_MOMENTUM),
                        nn.Upsample(scale_factor=2**(j-i), mode='nearest')))
                elif j == i:
                    # 本层不做处理
                    fuse_layer.append(None)
                else:
                    conv3x3s = []
                    # 进行strided 3x3 conv下采样,如果跨两层，就使用两次strided 3x3 conv
                    for k in range(i-j):
                        if k == i - j - 1:
                            num_outchannels_conv3x3 = num_inchannels[i]
                            conv3x3s.append(nn.Sequential(
                                nn.Conv2d(num_inchannels[j],
                                          num_outchannels_conv3x3,
                                          3, 2, 1, bias=False),
                                nn.BatchNorm2d(num_outchannels_conv3x3,
                                               momentum=BN_MOMENTUM)))
                        else:
                            num_outchannels_conv3x3 = num_inchannels[j]
                            conv3x3s.append(nn.Sequential(
                                nn.Conv2d(num_inchannels[j],
                                          num_outchannels_conv3x3,
                                          3, 2, 1, bias=False),
                                nn.BatchNorm2d(num_outchannels_conv3x3,
                                nn.ReLU(False)))
                    fuse_layer.append(nn.Sequential(*conv3x3s))
            fuse_layers.append(nn.ModuleList(fuse_layer))

        return nn.ModuleList(fuse_layers)

    def get_num_inchannels(self):
        return self.num_inchannels

    def forward(self, x):
        if self.num_branches == 1:
            return [self.branches[0](x[0])]

        for i in range(self.num_branches):
            x[i]=self.branches[i](x[i])

        x_fuse=[]
        for i in range(len(self.fuse_layers)):
            y=x[0] if i == 0 else self.fuse_layers[i][0](x[0])
            for j in range(1, self.num_branches):
                if i == j:
                    y=y + x[j]
                else:
                    y=y + self.fuse_layers[i][j](x[j])
            x_fuse.append(self.relu(y))

        # 将fuse以后的多个分支结果保存到list中
        return x_fuse


blocks_dict={
    'BASIC': BasicBlock,
    'BOTTLENECK': Bottleneck
}


class HighResolutionNet(nn.Module):

    def __init__(self, cfg, **kwargs):
        super(HighResolutionNet, self).__init__()

        self.conv1=nn.Conv2d(3, 64, kernel_size=3, stride=2, padding=1,
                               bias=False)
        self.bn1=nn.BatchNorm2d(64, momentum=BN_MOMENTUM)
        self.conv2=nn.Conv2d(64, 64, kernel_size=3, stride=2, padding=1,
                               bias=False)
        self.bn2=nn.BatchNorm2d(64, momentum=BN_MOMENTUM)
        self.relu=nn.ReLU(inplace=True)

        self.stage1_cfg=cfg['MODEL']['EXTRA']['STAGE1']
        num_channels=self.stage1_cfg['NUM_CHANNELS'][0]
        block=blocks_dict[self.stage1_cfg['BLOCK']]
        num_blocks=self.stage1_cfg['NUM_BLOCKS'][0]
        
        self.layer1=self._make_layer(block, 64, num_channels, num_blocks)
        stage1_out_channel=block.expansion*num_channels

        self.stage2_cfg=cfg['MODEL']['EXTRA']['STAGE2']
        num_channels=self.stage2_cfg['NUM_CHANNELS']
        block=blocks_dict[self.stage2_cfg['BLOCK']]
        num_channels=[
            num_channels[i] * block.expansion for i in range(len(num_channels))]
        self.transition1=self._make_transition_layer(
            [stage1_out_channel], num_channels)
        self.stage2, pre_stage_channels=self._make_stage(
            self.stage2_cfg, num_channels)

        self.stage3_cfg=cfg['MODEL']['EXTRA']['STAGE3']
        num_channels=self.stage3_cfg['NUM_CHANNELS']
        block=blocks_dict[self.stage3_cfg['BLOCK']]
        num_channels=[
            num_channels[i] * block.expansion for i in range(len(num_channels))]
        self.transition2=self._make_transition_layer(
            pre_stage_channels, num_channels)
        self.stage3, pre_stage_channels=self._make_stage(
            self.stage3_cfg, num_channels)

        self.stage4_cfg=cfg['MODEL']['EXTRA']['STAGE4']
        num_channels=self.stage4_cfg['NUM_CHANNELS']
        block=blocks_dict[self.stage4_cfg['BLOCK']]
        num_channels=[
            num_channels[i] * block.expansion for i in range(len(num_channels))]
        self.transition3=self._make_transition_layer(
            pre_stage_channels, num_channels)
        self.stage4, pre_stage_channels=self._make_stage(
            self.stage4_cfg, num_channels, multi_scale_output=True)

        # Classification Head
        self.incre_modules, self.downsamp_modules, \
            self.final_layer=self._make_head(pre_stage_channels)

        self.classifier=nn.Linear(2048, 1000)

    def _make_head(self, pre_stage_channels):
        head_block=Bottleneck
        head_channels=[32, 64, 128, 256]

        # Increasing the #channels on each resolution
        # from C, 2C, 4C, 8C to 128, 256, 512, 1024
        incre_modules=[]
        for i, channels in enumerate(pre_stage_channels):
            incre_module=self._make_layer(head_block,
                                            channels,
                                            head_channels[i],
                                            1,
                                            stride=1)
            incre_modules.append(incre_module)
        incre_modules=nn.ModuleList(incre_modules)

        # downsampling modules
        downsamp_modules=[]
        for i in range(len(pre_stage_channels)-1):
            in_channels=head_channels[i] * head_block.expansion
            out_channels=head_channels[i+1] * head_block.expansion

            downsamp_module=nn.Sequential(
                nn.Conv2d(in_channels=in_channels,
                          out_channels=out_channels,
                          kernel_size=3,
                          stride=2,
                          padding=1),
                nn.BatchNorm2d(out_channels, momentum=BN_MOMENTUM),
                nn.ReLU(inplace=True)
            )

            downsamp_modules.append(downsamp_module)
        downsamp_modules=nn.ModuleList(downsamp_modules)

        final_layer=nn.Sequential(
            nn.Conv2d(
                in_channels=head_channels[3] * head_block.expansion,
                out_channels=2048,
                kernel_size=1,
                stride=1,
                padding=0
            ),
            nn.BatchNorm2d(2048, momentum=BN_MOMENTUM),
            nn.ReLU(inplace=True)
        )

        return incre_modules, downsamp_modules, final_layer

    def _make_transition_layer(
            self, num_channels_pre_layer, num_channels_cur_layer):
        num_branches_cur=len(num_channels_cur_layer)
        num_branches_pre=len(num_channels_pre_layer)

        transition_layers=[]
        for i in range(num_branches_cur):
            if i < num_branches_pre:
                if num_channels_cur_layer[i] != num_channels_pre_layer[i]:
                    transition_layers.append(nn.Sequential(
                        nn.Conv2d(num_channels_pre_layer[i],
                                  num_channels_cur_layer[i],
                                  3,
                                  1,
                                  1,
                                  bias=False),
                        nn.BatchNorm2d(
                            num_channels_cur_layer[i], momentum=BN_MOMENTUM),
                        nn.ReLU(inplace=True)))
                else:
                    transition_layers.append(None)
            else:
                conv3x3s=[]
                for j in range(i+1-num_branches_pre):
                    inchannels=num_channels_pre_layer[-1]
                    outchannels=num_channels_cur_layer[i] \
                        if j == i-num_branches_pre else inchannels
                    conv3x3s.append(nn.Sequential(
                        nn.Conv2d(
                            inchannels, outchannels, 3, 2, 1, bias=False),
                        nn.BatchNorm2d(outchannels, momentum=BN_MOMENTUM),
                        nn.ReLU(inplace=True)))
                transition_layers.append(nn.Sequential(*conv3x3s))

        return nn.ModuleList(transition_layers)

    def _make_layer(self, block, inplanes, planes, blocks, stride=1):
        downsample=None
        if stride != 1 or inplanes != planes * block.expansion:
            downsample=nn.Sequential(
                nn.Conv2d(inplanes, planes * block.expansion,
                          kernel_size=1, stride=stride, bias=False),
                nn.BatchNorm2d(planes * block.expansion, momentum=BN_MOMENTUM),
            )

        layers=[]
        layers.append(block(inplanes, planes, stride, downsample))
        inplanes=planes * block.expansion
        for i in range(1, blocks):
            layers.append(block(inplanes, planes))

        return nn.Sequential(*layers)

    def _make_stage(self, layer_config, num_inchannels,
                    multi_scale_output=True):
        num_modules=layer_config['NUM_MODULES']
        num_branches=layer_config['NUM_BRANCHES']
        num_blocks=layer_config['NUM_BLOCKS']
        num_channels=layer_config['NUM_CHANNELS']
        block=blocks_dict[layer_config['BLOCK']]
        fuse_method=layer_config['FUSE_METHOD']

        modules=[]
        for i in range(num_modules):
            # multi_scale_output is only used last module
            if not multi_scale_output and i == num_modules - 1:
                reset_multi_scale_output=False
            else:
                reset_multi_scale_output=True

            modules.append(
                # 调用高低分辨率交互模块， stage2 为例
                HighResolutionModule(num_branches,  # 2
                                     block,  # 'BASIC'
                                     num_blocks,  # [4, 4]
                                     num_inchannels,  # 上个stage的out channel
                                     num_channels,  # [32, 64]
                                     fuse_method,  # SUM
                                     reset_multi_scale_output)
            )
            num_inchannels=modules[-1].get_num_inchannels()

        return nn.Sequential(*modules), num_inchannels

    def forward(self, x):

        # 使用两个strided 3x3conv进行快速降维
        x=self.relu(self.bn1(self.conv1(x)))
        x=self.relu(self.bn2(self.conv2(x)))

        # 构建了一串BasicBlock构成的模块
        x=self.layer1(x)

        # 然后是多个stage，每个stage核心是调用HighResolutionModule模块
        x_list=[]
        for i in range(self.stage2_cfg['NUM_BRANCHES']):
            if self.transition1[i] is not None:
                x_list.append(self.transition1[i](x))
            else:
                x_list.append(x)
        y_list=self.stage2(x_list)

        x_list=[]
        for i in range(self.stage3_cfg['NUM_BRANCHES']):
            if self.transition2[i] is not None:
                x_list.append(self.transition2[i](y_list[-1]))
            else:
                x_list.append(y_list[i])
        y_list=self.stage3(x_list)

        x_list=[]
        for i in range(self.stage4_cfg['NUM_BRANCHES']):
            if self.transition3[i] is not None:
                x_list.append(self.transition3[i](y_list[-1]))
            else:
                x_list.append(y_list[i])
        y_list=self.stage4(x_list)

        # 添加分类头，上文中有显示，在分类问题中添加这种头
        # 在其他问题中换用不同的头
        y=self.incre_modules[0](y_list[0])
        for i in range(len(self.downsamp_modules)):
            y=self.incre_modules[i+1](y_list[i+1]) + \
                self.downsamp_modules[i](y)

        y=self.final_layer(y)

        if torch._C._get_tracing_state():
            # 在不写C代码的情况下执行forward，直接用python版本
            y=y.flatten(start_dim=2).mean(dim=2)
        else:
            y=F.avg_pool2d(y, kernel_size=y.size()
                                [2:]).view(y.size(0), -1)

        y=self.classifier(y)

        return y

    def init_weights(self, pretrained='',):
        logger.info('=> init weights from normal distribution')
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                nn.init.kaiming_normal_(
                    m.weight, mode='fan_out', nonlinearity='relu')
            elif isinstance(m, nn.BatchNorm2d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)
        if os.path.isfile(pretrained):
            pretrained_dict=torch.load(pretrained)
            logger.info('=> loading pretrained model {}'.format(pretrained))
            model_dict=self.state_dict()
            pretrained_dict={k: v for k, v in pretrained_dict.items()
                               if k in model_dict.keys()}
            for k, _ in pretrained_dict.items():
                logger.info(
                    '=> loading {} pretrained model {}'.format(k, pretrained))
            model_dict.update(pretrained_dict)
            self.load_state_dict(model_dict)


def get_cls_net(config, **kwargs):
    model=HighResolutionNet(config, **kwargs)
    model.init_weights()
    return model
